Integrated circuits form the basis for many electronic systems. Essentially, an integrated circuit includes a vast number of transistors and other circuit elements that are formed on a single semiconductor wafer or chip and are interconnected to implement a desired function. The complexity of these integrated circuits requires the use of an ever increasing number of linked transistors and other circuit elements.
Many electronic systems are created through the use of a variety of different integrated circuits; each integrated circuit performing one or more specific functions. For example, computer systems include at least one microprocessor and a number of memory chips. Conventionally, each of these integrated circuits is formed on a separate wafer or chip, packaged independently and interconnected on, for example, a printed circuit board.
As integrated circuit technology progresses, there is a growing desire for a "system on a chip" in which the functionality of all of the integrated circuits of the system are packaged together without a conventional printed circuit board. Ideally, a computing system would be fabricated with all the necessary integrated circuits on one wafer, as compared with today's method of fabricating many chips of different functions and packaging them to assemble a complete system. Such a structure would greatly improve integrated circuit performance and provide higher bandwidth.
In practice, it is very difficult with today's technology to implement a truly high-performance "system on a chip" because of vastly different fabrication processes and different manufacturing yields for the logic and memory circuits.
As a compromise, various "system modules" have been introduced that electrically connect and package integrated circuit devices which are fabricated on the same or on different semiconductor wafers. Initially, system modules were created by simply stacking two semiconductor chips, e.g., a logic and memory chip, one on top of the other in an arrangement commonly referred to as chip-on-chip (COC) structure. Chip-on-chip structures most commonly use micro bump bonding technology (MBB) to electrically connect the working surfaces of two chips. Several problems, however, remain inherent with this design structure. For example, this approach is limited in the number of chips that can be interconnected as part of the system module.
Some researchers have attempted to develop techniques for interconnecting a number of chips in a stack to form a system module. However, these modules suffer from additional problems. For example, some modules use chip carriers that make the packaging bulky. Further, others use wire bonding that gives rise to stray inductances that interfere with the operation of the system module.
Thus, it is desirable to develop an improved structure and method for interconnecting integrated circuits on separate chips or wafers in a system module.